Conventional hydrometallurgical processes that utilise ion-exchange resins to extract non-ferrous metals from ore typically involve the non-ferrous metals being leached from the ore with a mineral acid solution to form a slurry. The slurry is then fed to a solid/liquid separator from which a solid phase and a clear pregnant liquid phase are discharged. The liquid phase is subsequently contacted with the ion-exchange resin in a metal recovery step. However, the solid/liquid separation step has proven to be problematic for a number of reasons that stem from the solid phase having a very fine particle size distribution.
Counter/current decantation (CCD) circuits are widely used for carrying out the solid/liquid separation step. Each circuit often includes a series of 6 to 9 thickeners, each in excess of 50 metres in diameter in order to minimise metal losses and produce a clear pregnant leach liquid phase. In addition, operational costs of the thickeners include power consumption for operating raking mechanisms, and water and flocculant consumption. The flocculant consumption often ranges from 200 to over 800 grams per tonne of solid extracted and may account for up to 10% of the total plant operating costs.
To avoid the intrinsic problems of CCD circuits, resin-in-pulp processes are being developed whereby valuable metals are first leached from the raw material to form a pregnant slurry and an ion-exchange resin is then used to directly absorb the valuable metals from the slurry rather than from the clear pregnant leach solution. Loaded resin can then be separated from the pulp and the valuable metals desorbed from resin to enable reuse of the resin.
In order for the exchange resin to be viably used in resin-in-pulp processes on the commercial basis, the resin must both preferentially absorb the valuable metals and have adequate hydro-mechanical strength and durability so that it can be repeatedly used in pulp processing equipment.